1. Field of Invention
This invention relates to electrical and electronic circuits and systems. Specifically, the present invention relates to systems and methods for improving the dynamic range of circuits, such as radar and Radio Frequency (RF) communications receivers.
2. Description of the Related Art
Receivers are employed in various demanding applications including radar, ladar, and microwave sensing systems. Such applications demand receivers that can accommodate various signal magnitudes including both faint and intense signals without causing signal distortion, such as spurs, clipping, or intermodulation distortion. This necessitates receivers with high dynamic ranges, preferably above 100 dB. High dynamic range receivers are particularly important in communications systems and projected munition targeting applications, where sufficient system resolution and signal detection capability are required to extract desired signals from background noise and other signal clutter.
Conventionally, receiver dynamic range is increased by improving receiver components, such as Analog-to-Digital Converters (ADC's). Unfortunately, dynamic ranges of ADC's are improving somewhat slowly. Furthermore, high dynamic range ADC's require accompanying high-performance components, such as mixer/amps, which may be prohibitively expensive or unavailable. Accordingly, conventional receiver design methods are often incapable of achieving receiver dynamic ranges above 60 dB.
To enhance receiver performance, receive signal levels may be adjusted to reduce false signal defects (spurs), receiver saturation, and signal clipping caused by excessively large signals. Video levels are lowered so that signal spikes do not saturate the ADC or accompanying components. Unfortunately, lowering video levels may compromise receiver ability to detect faint signals and to extract desired signals from background noise or ground clutter.
To address problems in the detection of faint signals in intense signal environments, Automatic Gain Control circuits (AGC's) are often employed for automatically controlling input video levels. AGC's may reduce signal spurs caused by excessively large signals. An AGC automatically adjusts average receive signal levels to avoid frequent ADC saturation and associated signal spurs, which compromise receiver performance. Unfortunately, valuable signal magnitude information is often lost by AGC video adjustment. For example, the original magnitude of a large attenuated input signal may be unknown after attenuation, and faint signals among large signals may become undetectable. AGC's typically do not increase the effective dynamic range of accompanying ADC's.
Alternatively, sliding scale attenuators are employed to improve receiver performance. An exemplary sliding scale attenuator includes three banks, each bank having three voltage comparators. The banks determine signal attenuation values to facilitate ADC operation. The sliding scale attenuator selects a desired signal attenuation from nine calculated attenuator values, one for each comparator, based on predetermined selection rules. Unfortunately, the sliding scale attenuator is relatively slow, cannot optimize the dynamic range of the ADC, and causes loss of signal magnitude information.
Hence, a need exists in the art for an efficient system and method for improving the dynamic range of a circuit without necessitating the loss of signal magnitude information.